1. Field of the Invention
The present invention relates generally to high-frequency distribution circuits and particularly to high-frequency distribution circuits distributing to a plurality of output terminals a frequency signal received at an input terminal.
2. Description of the Background Art
FIG. 19 is a block diagram showing a configuration of a receiving unit of a satellite broadcast system as conventional. In FIG. 19 the satellite broadcast system has the receiving unit including an antenna 103 having a reflector 101 and a low noise block down converter (LNB) 102, receivers (or load circuits) 104 and 105, and television sets 106 and 107.
A satellite emits an electric wave α which is received via reflector 101 by LNB 102. LNB 102 extracts video signals of a plurality of channels from the received electric wave α and also amplifies the video signals with minimized noise, and provides receivers 104 and 105 with video signals (or high-frequency signals) of the channels selected by receivers 104 and 105, respectively. LNB 102 outputs a signal which is in turn FM-demodulated in each of receivers 104 and 105 and furthermore converted to video and audio signals and provided to television sets 106 and 107. Television sets 106 and 107 display on their screens the video images of the channels selected by the tuners of receivers 104 and 105, respectively (see for example Japanese Patent Laying-Open No. 2002-218329).
Such LNB 102 is provided therein with a high-frequency distribution circuit distributing a video signal to the two receivers 104 and 105, and its power supply voltage is supplied from receivers 104 and 105.
The characteristic impedance of a coaxial cable connected to each output terminal of such LNB 102, switch (SW)-BOX and the like, and the input impedance of receivers 104 and 105 are typically 75Ω. As such, if in LNB 102 or the like a received signal is monitored at one output terminal and the other output terminal has nothing connected thereto, then at the other output terminal the received signal is totally reflected. Thus whether the other output terminal is connected or not provides a difference in level of a received signal monitored at one output terminal, poor isolation, and other similar disadvantages.
If any unused output terminal is terminated by a termination of 75Ω, the variation in impedance attributed to whether the output terminal is used or not can be eliminated. Providing the LNB, the SW-BOX or other similar products with a termination as an accessory, however, is significantly costly.
A final-stage amplifier or the like may have an attenuator inserted therein to attenuate in level a signal reflected from an output terminal. This, however, requires that the amplifier be increased in gain, which can result in increased current consumption, poor phase noise, and/or similar detriments.